Articles: hyperalgesia.
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This study aimed to examine the association of hemiplegic shoulder pain (HSP) with central hypersensitivity through pressure-pain thresholds (PPTs) in healthy, distant tissues. ⋯ The subjects with HSP have lower local and distal PPTs than the subjects without HSP. This study suggests that chronic shoulder pain may be associated with widespread central hypersensitivity, which has been previously found to be associated with other chronic pain syndromes. This further understanding can then help develop better treatment options for those with this HSP.
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Immunohistological analysis of spinal glial cells and analysis of pain behavior in the rat neuropathic pain model were investigated to clarify the function of tumor necrosis factor (TNF)-α receptors p55 type 1 and p75 type 2. ⋯ These results indicate that the microglial TNF-α p55 pathway played a more important role than the TNF-α p75 pathway in the pathogenesis of peripheral nerve injury pain. This suggests that future studies seeking to clarify neuropathic pain should target TNF-α and p55 receptors in microglia.
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Despite the subjective nature of pain experience with cognitive and affective dimensions, preclinical pain research has largely focused on its sensory dimension. Here, we examined the relationship between learning/memory and nociceptive behavior in rats with combined learning impairment and persistent nociception. Learning impairment was induced by bilateral hippocampal injection of a mixed Aβ solution, whereas persistent nociception produced in these rats by complete Freund's adjuvant-induced ankle inflammation. ⋯ Moreover, expression of Aβ, NR1 subunit of the N-methyl-D-aspartate receptor, and protein kinase Cγ was upregulated, whereas the choline acetyl transferase expression was downregulated, in the hippocampus, thalamus, amygdala, and/or spinal cord of rats with combined learning impairment and persistent nociception. The data indicate that learning impairment could disrupt the response to a state of persistent nociception, suggesting an important role for cognitive maladaptation in the mechanisms of chronic pain. These results also suggest that a preclinical model of combined learning impairment and persistent nociception may be useful to explore the brain mechanisms underlying the transition from acute to chronic pain.
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Randomized Controlled Trial
Amygdala activity contributes to the dissociative effect of cannabis on pain perception.
Cannabis is reported to be remarkably effective for the relief of otherwise intractable pain. However, the bases for pain relief afforded by this psychotropic agent are debatable. Nonetheless, the frontal-limbic distribution of cannabinoid receptors in the brain suggests that cannabis may target preferentially the affective qualities of pain. ⋯ Critically, the reduction in sensory-limbic functional connectivity was positively correlated with the difference in drug effects on the unpleasantness and the intensity of ongoing pain. Peripheral mechanisms alone cannot account for the dissociative effects of THC on the pain that was observed. Instead, the data reveal that amygdala activity contributes to interindividual response to cannabinoid analgesia, and suggest that dissociative effects of THC in the brain are relevant to pain relief in humans.
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Opioids have been the mainstay analgesics for postoperative, cancerous, and chronic noncancerous pain. Common concerns regarding the use of opioids include the development of physical dependence and addiction. However, as a potential complication of opioid therapy, opioid-induced hyperalgesia (OIH) is often overlooked. ⋯ We present 2 cases of OIH resulting from administration of tramadol, which is a synthetic analogue of codeine and exhibits 10-fold less affinity for mu-opioid receptors, in patients suffering from chronic pain. The 2 cases presented herein imply the importance of recognizing OIH in patients medicated with tramadol if analgesic effects are lost in the context of dose titration, when generalized pain is reported without any evidence of disease exacerbation. While OIH associated with ultra-low dose opiates seems to be quite rare, if it is suspected, switching to other drugs and an appropriate treatment should be considered.